The invention relates to methods and systems for measuring the tension in a rod, bolt, tendon or like body that is anchored or attached adjacent to one end that is not accessible and that is accessible for measurement at an opposite end. The rod or bolt may be longer than 5 to 10 feet such that direct use of an ultrasonic transducer to measure bolt length as a method to estimate bolt tension in a metal body is not effective. The new method may attach a relatively short representative bolt to the accessible end of a relatively longer anchored bolt that is generally inaccessible that may be embedded in cement, concrete, rock or other material.
Methods and apparatus may currently be known that use ultrasonic waves or vibrations to investigate rod-like bodies that may be embedded and anchored in surrounding material such as concrete, rock or other material such that the rod cannot be directly accessed at both ends and along its length. Instruments that measure elongation of a bolt while it is being tensioned/torqued that use ultrasonic's may be known. These instruments are tension bolting control systems that depend upon measuring changes in length between the unloaded and the loaded or stressed conditions of a particular fastening device, such as a bolt, while being torqued/stretched to evaluate tension. All of these type methods and apparatus may generally be useable only for short lengths of metal bolts, rods, or tendons i.e., 4 to 5 feet or less in length.
To investigate longer rod or bolt conditions, for example, bolts of 30 feet or longer, other techniques may be used than ultrasonic bolt length measurement. An example of one method that may be used for long bolts that are used for attaching a structure, for example a wind electric generator tower, to an earth embedded concrete foundation may be to use a torque wrench device to test the torque force present at an upper nut tightened on the flange of the tower base. While this may be a current practice for estimating tension on an attachment bolt, the torque devices are not accurate devices and may allow for a wide variance in estimates by a technician in recording bolt tension conditions.